The number of echoes combined into a single image or image set in multiple echo imaging sequences or echo-train techniques such as rapid acquisition with relaxation enhancement (RARE), fast-spin echo (FSE), and turbo spin-echo (TSE). In RARE imaging, the ETL typically equals the acceleration factor.
As for tooth pain, it is caused by a reaction of the nerves inside a tooth's pulp chamber with the severity dependent upon the type and degree of the stimulus. What follows are some examples of symptoms you may be feeling and their possible causes.
Other causes of tooth pain: 1  Food getting stuck between your teeth, especially if your teeth have spaces in between them. 2  Trauma to the tooth, including injury or grinding your teeth. 3  A sinus infection that can be felt as pain in the teeth.